<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>盒子</title>
</head>
<style>
.box{
    width: 500px;
    border: 10px red double;
    height: 500px;
    margin-top: 200px;
    margin-left: 200px;
    padding-left: 100px;
    padding-top: 100px;
    border-radius: 50%;
    background-color: lightblue;
}

body{
    border: 1px green solid;
}
</style>
<body>
  <p class="box">盒子</p>  
</body>
</html>